Currently gold-containing materials such as gold ores and concentrates are almost exclusively subjected to cyanide leaching for recovery of gold. However, in non-free-milling gold-containing materials such as refractory ores and concentrates gold particles are in locked within a matrix, most commonly sulfidic minerals, and cyanide solution cannot break up the sulfide structures such as pyrite (FeS2) and/or arsenopyrite (FeAsS). Thus pretreatment is necessary to decompose the mineral structure to liberate gold for subsequent recovery. Typically gold-containing refractory sulfidic materials is preprocessed before leaching by pressure oxidation (POX) to facilitate the recovery of gold at economic scale. There are also processes recovering gold using halide media from sulfidic or other gold-containing materials. However, presence of refractory sulfidic materials decreases gold recovery also in these processes.
In pressure oxidation sulfidic minerals are oxidized exposing encapsulated gold and liberating it into solution for subsequent recovery by leaching. The POX process takes place in an autoclave in harsh conditions at high temperature and high pressure. The cost of such autoclave equipment is high and often the autoclave capacity limits the processing capacity of the gold processing plant.
To maintain the heat and acid balance the POX process also requires certain sulfur content in the treated material. The sulfur content can be adjusted before the POX processing by processing all or part of the material in a sulfide flotation process where material having low sulfur content is removed as flotation tailings and the flotation concentrate is reported to the POX.
WO2013110757A1 discloses a method for enrichment of metal sulfide ores in desired minerals in cases where the ores have sulfide-containing gangues by addition of an oxidant to slurries prepared from the ores during or immediately prior to froth flotation without any conditioning of the pulp.
U.S. Pat. No. 6,210,648 B1 discloses a method for flotation of refractory auriferous sulfides using an oxygen-deficient flotation gas for a non-selective flotation of different iron-containing sulfide mineral species prior to POX. The method promotes the flotation of the refractory auriferous sulfides and claims to enhance separation of sulfide minerals, including refractory auriferous sulfides, from non-sulfide gangue material. The flotation concentrates are recovered from the flotation froth enriched in sulfide minerals. However, the method does not allow selective separation of sulfidic minerals from each other.